It is common practice to provide aerofoil blades or vanes for use in the turbines of gas turbine engines with some form of cooling in order that they are able to operate effectively in the high temperature environment of such turbines. Such cooling typically takes the form of passages within the blades or vanes which are supplied in operation with pressurised cooling air derived from the compressor of the gas turbine engine.
In such arrangements the cooling air is directed through passages in the blade or vane to provide convective and sometimes impingement cooling of the blade or vane's internal surfaces before being exhausted into the hot gas flogs in which the blade or vane is operationally situated. The cooling air may also be directed through small holes provided in the aerofoil surface of the blade or vane to supply a film of cooling air over the external surface of the aerofoil to provide film cooling of the aerofoil surface.
It is known to form such passages as one convoluted passageway which allows a length/diameter ratio to be utilised providing an acceptable degree of cooling efficiency. However, such a convoluted passageway necessarily requires bends which give rise to pressure losses without heat transfer. Also each bend requires a hole to be formed through which debris within the cooling air be exhausted.